1. Field of the Invention
The present invention provides an apparatus and method for injecting fluid into a balloon catheter and a device for controlling the rate and pressure of fluid injection. Such catheters, when inflated by the injected fluid, are conventionally used for the purpose of percutaneous transluminal angioplasty.
Angioplasty is a procedure for dilating arteries which are occluded or blocked. It is done primarily on femoral (thigh) and renal (kidney) obstructions, and in some cases on coronary artery obstructions. A special catheter is used which contains a sausage-shaped segment or balloon at the distal end. To re-shape an occluded artery, the balloon portion is inflated, for instance, by being filled and pressurized with diluted contrast media.
2. Description of the Prior Art
An early practitioner of the angioplasty procedure was Dr. Andreas Gruntzig of the University of Zurich. The procedure developed by Dr. Gruntzig uses a special double lumen catheter. The first lumen allows passage of a guide wire and contrast media, like a conventional catheter. The second lumen connects to a sausage-shaped segment or balloon at the distal end of the catheter, which is generally filled and pressurized with diluted contrast media. Briefly, the procedure involves inserting a guide wire into a blood vessel to be dilated and advancing the guide wire to and past the block. Next, a balloon catheter is inserted along the guide wire and advanced to the most distal portion of the block or occlusion. Then, the balloon is inflated to reform the blockage material against the artery wall. The dilated balloon creates a smooth increased-diameter inner lumen in the artery. After dilation, the balloon is collapsed and retracted. The site of the former obstruction is examined, and, if necessary, the procedure is repeated until the entire segment of the artery is dilated.
The purpose of an angioplasty injector is to make the balloon inflation task easier and safer. One conventional procedure is to use a syringe to expand the balloon with radiopaque dye, while watching the balloon on an x-ray monitor. An operator proceeds by judging the relative balloon size, without knowing the balloon pressure; however, the balloon may rupture if its bursting pressure is exceeded.
A first approach to solving the problem of measuring the pressure of fluid inflating the balloon, i.e., syringe fluid pressure, is to interpose a T-fitting between the delivery end of the syringe and the balloon. A tire pressure-type gauge or other pressure indicator is connected to the T-fitting in such manner that the gauge comes in direct contact with the fluid, as it leaves the syringe, and measures the pressure exerted by the fluid.
One such system uses a slider that moves out of a housing with an increase in pressure and retracts into the housing with a decrease in pressure. Since a moving part of the gauge directly contacts the media solution, cleaning and sterilization of the gauge is required.
A second approach using a T-fitting for measuring syringe fluid pressure is to interpose a gauge using a separate pressure sensing member or disposable diaphragm positioned between the delivery end of the syringe and the balloon. One end of the diaphragm is contacted by the media fluid entering the balloon, while the other end acts on a pressurizing fluid associated with a gauge. This approach, like the first approach, uses a member directly contacted by the media fluid.
A problem encountered with use of a T-fitting or with use of a pressure sensing member directly contacted by the contrast media solution is that the contrast media solution used to inflate the balloon must be removed by thorough cleaning after each use. Such cleaning involves disassembly, cleaning, and sterilization. If the contrast media is not thoroughly removed, it becomes gummy as it dries, and, when fully dry, is hard like varnish. This can interfere with proper gauge operation. A gauge thus damaged could read improper pressures and mislead an operator.
A third approach to controlling media fluid pressure uses a pressurized carbon dioxide cartridge. The control system includes a pressure control, forward-reverse switch, and a conventional gauge arrangement. This approach uses a syringe and gauge that must be disassembled for cleaning. A problem with this approach is the need to provide a carbon dioxide cartridge, and the system can be expensive.
Several problems have been encountered with the previously described approaches. These problems include the need to carefully clean the measuring systems and gauges when the gauges or movable members associated with the gauges are directly contacted by the media fluid. Some of the approaches also require constant operator pressure on the syringe plunger to maintain dilation of the balloon. Some of the approaches rely solely on direct manual movement of the syringe plunger by the operator to obtain a desired pressure. With the exception of the system using the carbon dioxide cartridge, no provision is made for fine adjustment of pressure or for holding a desired pressure. Further, some of the gauges record only present pressure and do not record maximum inflation pressure achieved during an inflation cycle.